U.S. Pat. No. 5,098,637 discloses a method and system for injection molding hollow plastic articles with pressurized gas which provides for displacement by the gas of a portion of plastic from the mold cavity into a flow-coupled spill cavity. The volume of the spill cavity may be varied to control the quantity of displaced plastic such as by a lead screw.
U.S. Pat. No. 5,607,640 (i.e. '640 patent) discloses in FIGS. 1-4 thereof, the use of a spill cavity with a blocking pin and shims to control the volume of plastic going into the spill cavity. The pin is in its up position to block plastic flow from the article-defining cavity, through a runner and into the spill cavity. Subsequently, the pin moves to its down position to allow plastic to go to the spill cavity by pressurized gas. In the remainder of the '640 patent, a method and system are disclosed where the volume of the spill cavity is allowed to increase in a controlled fashion to a final volume based on the amount of plastic injected into the mold cavity. The volume of the spill cavity increases during a step of displacing the plastic into the spill cavity. In this way, the method and system eliminate the need for a shut-off or blocking pin. In two disclosed embodiments, pistons are utilized to purge or displace plastic from the spill cavity.
European Patent Document No. 393,315 discloses a spill subgate with a blocking hydraulic pin.